Search engines all have best practices in terms of how long your meta description should be, or how many characters should be in your title tag.
As I measure these out, I find myself turning to Twitter more and more often! Their interface for tweets makes it really easy to see how many characters you have typed out. Just take 140 minus characters remaining and you’ve got the number of characters in your sentence.
I am now using Twitter to ensure our clients have their most important information within these seo character guidelines:
Meta description recommended length: 160 characters
Title tag recommended length: 60 characters
Recommended Keywords: 5 per page